1. Field of the Invention
This invention relates generally to automatic data cartridge feeders for use with drive units and, more particularly, to automatic cartridge feeders that receive cartridges and transport them to and from a drive unit for processing.
2. Description of the Related Art
Computer system tape drive units can be configured to receive tape cartridges, such as IBM Corporation 3480 and 3490E cartridges. The cartridges contain a length of magnetic tape upon which data can be written and read. Many tape drive units can mate with an automatic cartridge feeder that accepts a tape cartridge and transports it to the drive unit tape transport mechanism and read/write heads. Automatic cartridge feeders are available in configurations that accept cartridges one at a time through a single feed slot and configurations that mate with removable cartridge magazines, containing a plurality of tape cartridges, from which cartridges are accepted one at a time.
Automatic cartridge feeders having a feed slot for single cartridges permit an operator to sequentially insert tape cartridges that are automatically transported to the drive unit. In this way, the operator has complete control over the next cartridge to be processed and can interrupt a planned sequence of cartridges at any time to insert a high priority cartridge or to otherwise process a cartridge out of turn. An automatic cartridge feeder with only a single feed slot can be very inefficient, however, because an operator is occupied substantially the entire time the drive unit is being used. Moreover, loose cartridges can be lost, mishandled, or placed out of sequence.
Automatic cartridge feeders that accept removable cartridge magazines can greatly increase operating efficiency. A cartridge magazine typically includes a plurality of cartridge shelves, each of which receives a cartridge, and is coupled to the cartridge feeder such that the cartridge feeder can transport cartridges from the magazine to the drive unit in the sequence they are stored in the magazine or in a sequence selected by the drive unit. Typical magazines have a capacity of seven to twelve cartridges. The cartridge magazine frees an operator from being occupied with the feeder and drive unit and also reduces the number of times an operator must manually intervene to provide fresh cartridges. Unfortunately, once a cartridge magazine is mounted to a cartridge feeder, there is no quick and efficient way to process a particular priority cartridge that is not already in the magazine. Typically, an operator must remove the magazine, insert a desired cartridge in the next shelf to be processed, and replace the magazine back with the cartridge feeder. It therefore is necessary to know which cartridge will be processed next so it can be removed and replaced with the desired priority cartridge. It can be very difficult to carry out such remove and replace operations without interfering with ongoing tape operations. Thus, unlike an automatic cartridge feeder with a single feed slot, an automatic cartridge feeder with a magazine can make if difficult to get a particular tape cartridge to be used next.
It is known to designate one shelf of a cartridge magazine as a priority shelf. See, for example, the Laser Magnetic Storage International Company Hardware Maintenance Manual for their Independence-brand Cartridge Tape Subsystem. In a typical cartridge feeder with a magazine having a designated priority shelf, the feeder can be operated in a priority mode, in which a cartridge that is unprocessed and is on the priority shelf (a "priority cartridge") will be the next cartridge processed after processing of a current cartridge is completed, and also in a sequential mode, in which all shelves of the magazine are processed in sequence. In the priority mode, after the priority cartridge is processed, the remaining cartridges in the magazine are processed in accordance with normal operation. To insert a cartridge for priority processing, access to the magazine shelves is first achieved by opening an access door, unlocking the shelves, or otherwise permitting access to the magazine shelves.
If the feeder is operated in sequential mode and a priority cartridge must be processed out of turn, any cartridge placed on the priority shelf of the magazine as part of the predetermined sequence of cartridges to be processed must be removed before the priority cartridge is inserted into the priority shelf and the operating mode is changed. This destroys any predetermined sequencing of the cartridges in the magazine. It also provides an opportunity to lose or mishandle the cartridge removed from the magazine, which now has no convenient place for safekeeping. These problems can be avoided by reserving one shelf at all times for use only as the priority shelf. Reserving one magazine shelf as a priority shelf, however, reduces the effective cartridge capacity of the magazine. Conversely, it can be cumbersome and time-consuming to process a priority cartridge if all of the magazine shelves are routinely used for predetermined cartridge sequences and no shelf is reserved as a priority shelf.
As noted above, removable cartridge magazines increase efficiency by freeing an operator from attending to the automatic cartridge feeder and drive unit. Automated cartridge library systems include a robot that loads cartridges onto moving belt, which carries the cartridges one at a time to a cartridge feeder having a single feed slot. The robot can retrieve cartridges from a cartridge library and deliver them to the belt without operator intervention, thereby increasing efficiency. It would be advantageous if a robot-operated automatic cartridge library system could use feeders that are compatible with cartridge magazines. In this way, the advantages of cartridge magazine feeder systems over single feed slot feeder systems could be extended to cartridge library systems. Conventional feeder systems that are compatible with cartridge magazines are not compatible with robot-operated cartridge library systems. Conventional cartridge magazine feeder systems include access doors and magazine lock bars to ensure cartridge magazine integrity. These features, as well as other configuration details, make such systems incompatible with robot-operated cartridge library systems.
From the discussion above, it should be apparent that there is a need for an automatic cartridge feeder with magazine loading that permits single feeding of cartridges without reducing effective magazine capacity and without altering a predetermined sequence of cartridges in the magazine when priority processing is desired and that also is compatible with automated cartridge library systems. The present invention satisfies this need.